You want to generate errors and warnings in your modules, but when you use
warn
or
die
, the user sees your own filename and line number. You'd like your functions to act like built-ins and report messages from the perspective of the user's code not your own.

Like built-ins, some of your module's functions generate warnings or errors if all doesn't go well. Think about
sqrt
: when you pass it a negative number (and you haven't used the Math::Complex module), an exception is raised, producing a message such as
"Can't
take
sqrt
of
-3
at
/tmp/negroot
line
17"
, where
/tmp/negroot
is the name of your own program. But if you write your own function that
die
s, perhaps like this:

then the message will say it's coming from the file your
even_only
function was itself compiled in, rather than from the file the user was in when they called your function. That's where the Carp module comes in handy. Instead of using
die
, use
croak
instead:

If you just want to complain about something, but have the message report where in the user's code the problem occurred, call
carp
instead of
warn
. (
carp
and
croak
do not share
warn
's and
die
's sensitivity to a trailing newline on the message.) For example:

Many built-ins emit warnings only when the
-w
command-line switch has been used. The
$^W
variable (which is not meant to be a control character but rather a
^
followed by a
W
) reflects whether that switch was used. You could choose to grouse only if the user asked for complaints:

carp "$n is not even, continuing" if $^W;

Finally, the Carp module provides a third function:
confess
. This works just like
croak
, except that it provides a full stack backtrace as it dies, reporting who called whom and with what arguments.